An aspect of the present invention relates to a magnet assembly for a plasma process chamber.
In the fabrication of integrated circuits (ICs) and displays, a number of processes are performed on a substrate in a plasma process chamber, including the deposition and etching of layers on the substrate. Typically, the process chamber comprises a substrate support, a gas distributor, a gas energizer to form a plasma from gas, and a gas exhaust. In such chamber, a magnet assembly can also be used to generate a magnetic field about a substrate processing zone in the chamber, to for example, limit the passage of charged plasma species into an exhaust port that is part of the gas exhaust, or to control the distribution or movement of plasma species across the substrate surface. The magnet assembly is typically positioned about the chamber, for example, on a wall around the substrate support such as an external chamber wall or liner.
One type of magnet assembly comprises a housing holding a number of magnets, as described in commonly assigned U.S. patent publication No. U.S.-2003-0192646-A, filing on Apr. 12, 2002, entitled “Plasma Processing Chamber Having Magnet assembly and Method,” which is incorporated herein by reference in its entirety. The housing is U-shaped to fit around a number of magnets, and is sealed by a cover plate that is welded along the open edges of the U-shaped housing. However, such magnet assemblies can be unreliable during operation. The weld seam of the housing often develops microcracks or holes with thermal cycling in the chamber, and the plasma in the chamber permeates through these holes and cracks to degrade the housing and magnets. This can have undesirable effects on the substrate being processed and the ability of the magnet assembly to contain the plasma.
Magnet assembly housings sealed by a cover plate can also be difficult to fabricate or assemble. Welding the cover plate typically involves subjecting the magnet assembly contained in the housing to high temperatures that can demagnetize or thermally degrade the magnets. It is also difficult to maintain the magnets aligned in the housing while the cover plate is being welded on to the housing. Often, some of the magnets become misaligned during assembly and this results in the magnet assembly providing an undesirable magnetic field distribution.
Furthermore, when the assembled housing is subjected to an anodizing treatment to form a protective anodization layer on the housing, the anodizing treatment material can permeate thorough any fine microcracks or holes in the weld seam to enter into the housing. The magnets can be eroded or otherwise degraded by the anodization treatment material. Also, during chamber processing, the trapped anodization material can vaporize to outgas into the vacuum environment of the chamber, affecting the substrate process.
Thus, it is desirable to have a magnet assembly that is more resistant to plasma erosion. It is further desirable to have a magnet assembly that allows easier assembly and alignment of the magnets in the housing without damaging their magnetic properties.